Best out-of-the-box 10V reference?

[Muxr]

Hello,

Mhm, there should be also a 5 V output to distinguish ageing of the reference and ageing of the rest of the cirquit.
I guess that that drift what you see is not the ageing of the reference.

With best regards

Andreas

Good point, aging of the reference [board] as a whole, not the actual chip, thanks.

[0.01C]

In the bbs.38hot.net forum , there are some people diy 10V reference kit for sell (price $100-$250 only), I bought three SZA263 10V(@$200 full set) and one LTZ pwm 10V (free from my friend),
very good 

http://bbs.38hot.net/search.php?mod=forum&searchid=396&orderby=lastpost&ascdesc=desc&searchsubmit=yes&kw=10V+%BB%F9%D7%BC

http://bbs.38hot.net/forum.php?mod=viewthread&tid=174007&extra=&page=1

http://bbs.38hot.net/forum.php?mod=viewthread&tid=147708

http://bbs.38hot.net/forum.php?mod=viewthread&tid=111481

http://bbs.38hot.net/forum.php?mod=viewthread&tid=191238&highlight=10V%2B%BB%F9%D7%BC

http://bbs.38hot.net/forum.php?mod=viewthread&tid=133516&extra=&highlight=10V%2B%BB%F9%D7%BC&page=1

http://bbs.38hot.net/forum.php?mod=viewthread&tid=108021&highlight=10V%2B%BB%F9%D7%BC

update : I just contact with my friend ,he can offer eevblog member at ¥1000 for a LTZ PWM 10V kit ,but only 2 pcs .
PS : If this is not permit here ,please let me know ,Thanks

[agaelema]

Hi lars, could you explain the operation of the trim circuit using the NTC. I developed one reference using the REF102A (not the best) with other 4 multiple voltages (5, 2.5, 1.25, 0.625) using some INA2133. I think that circuit can be implemented in the REF102, I'm correct?

Can you indicate some texts about this TC circuit?

Thanks! 

What I have preferred the last years are actually the AD587 JQ as the LQ isn´t available. That the KQ and LQ isn´t available and that the UQ seems to be trimmed in another way is one reason I think it reasonable to believe a lot of JQ’s will be within 5ppm/C. And of course, I was lucky to get all my AD587JQ within +-5ppm/C. I have nine AD587JQ’s of date codes 1028, 1247, 1517 and 1609 bought from Digikey and RS components.

The datasheet for the AD587JQ says 20ppm/C temperature coefficient and that with the box method. So, at 25C you can have even worse TC. As I, Andreas, Joe Geller and a report from the LISA-project shows the AD587UQ has more like 7-11ppm/C at 25C but the box specification is 5ppm/C.

Joe used the LQ and I think all had the date code 0045. Most of the LQ Joe had were around +2ppm/C at 25C so the simple add-on with a NTC+ resistor worked well.

 I have temperature compensated many 10V references at home (never in a design at work) with NTC’s but mostly used other designs than the SVR-T design. The SVR-T design was just because the trimpot value was already fixed. Enclose a sketch for what I tried to describe earlier as an example for a more general design. It will give an adjustment range to compensate -8ppm/C to +12ppm/C. In this design the sensitivity to drift of all trim components are quite low compared to the SVR-T design. If I know the AD587 have a slight positive TC I can calculate a larger value instead of 1.5M to get less range and some second order compensation. Most AD587 seems to have a slight negative second order component of about -0.03ppm / (°C * °C) around 25C so a larger resistor gives some compensation for this. 1.5M together with 1.36M NTC gives a quite linear compensation, so no second order compensation, but useful for a broad range. I myself has set up an excel sheet for calculation of the NTC compensation.

That I say I prefer the AD587JQ is only true from a hobbyist point and to get a good “transfer standard” to compare and maintain 10V. In my professional work as a design engineer I haven’t designed in an AD587JQ and probably will not. Long long ago I designed in AD688AQ and BQ as they were good choices for +-10V refs with reasonable accuracy in data acquisition systems. As the AD588BQ are similar I guess it is a good choice for 15EUR/USD from eBay if they are not fake. My experiences with AD688xQ compared to AD587xQ are that the 587 is slightly more stable over time and draw much less power (10x) and don´t need dual supplies, so if you don’t need +-10v I prefer the AD587 in all aspects. Having just 2mA current draw is a plus when using say two 9V batteries to power your reference. Today most volt refs I design in are 2.5-5V in SMD of course.

Why 10V even for a hobbyist? I should say because of the traceability chain and uncertainties. If you, like me, after some years comes below 10ppm uncertainty the extra step from say 5 or 7.xV gives extra uncertainty. Not all have a super linear 8 ½ digit DMM or a KVD. My best DMMs are only 6 ½ digits and I never paid more than 100USD for a DMM yet. If you go for a couple of 10V references adjusted close to 10V it is also easy to make a simple x100 amplifier and with just a 3 ½ digit DMM to get 0.1ppm resolution when you regularly compare your references. Of course, after a while you will find it is difficult to measure the absolute long-term drift without repeated calibrations with known uncertainties. But even before that you have learned a lot about drifts between your samples. And temperature coefficients can be checked and adjusted with simple means. My first NTC temperature compensated REF102CM’s I adjusted with just a lamp above the DUT and a 3 ½ digit DMM + amplifier. Three out of four are below 0.1ppm/C at 23C. The fourth I must have made some mistake as it is +0.4ppm/C but as I have a second 10K NTC connected to banana jacks on the front of the box it is easy to compensate afterwards. Some other of my references aren’t compensated but I only compensate afterwards. I prefer the 10V adjusted to within say +-100ppm but some of my better reference have up to 400ppm offset (and 2ppm/C).

As Andreas pointed out you cannot temperature compensate away all TC on the IC. My estimate is maybe 10-20 times for a reference with about 5ppm/C from my experiences with an NTC very close to the IC (and of course mounted in a box, so outside gradients will not affect so much).

As the thread started with suggestion for 10v for MML I would say: DIY with AD587JQ and/or VREF10-003 from voltagestandard.com if you can afford 53USD for it. With the VREF10-003 you get 30ppm for 6 months and as far as I know it is a serious offer compared to many other Vref boards or boxes on eBay. I have only one VREF10-003 but at arrival it was very close and now after more than 1 year it is still just +12ppm. Of course it is humidity sensitive as all plastic refs. It has a cut-out on three sides of the IC but I am not so sure it helps. I think the humidity sensitivity comes from the epoxy in the DIP8 package. Enclose my measurements of it. The result is compensated for temperature (1.3ppm/C).

Having at least three 10V refs is nice as you can compare them. I try to compare my 10V refs each second or third month as that give multiple points over a year, which is nice to see seasonal variations.

Lars

A note: I usually say just “uncertainty” but more mean “expanded uncertainty” as it often is written in calibration protocols with k=2 or a confidence of 95%.

[Andreas]

Hello,

Lars cirquit is optimized for the AD587:

The trim range on AD587 is not symmetrically (-1 .. +3 %) thats why it is a advantage (for the T.C. adjustment) to put the trimmers in series.

For the REF102 the trim range is symmetrically (+/-3%) so it might be better to switch the trimmers in parallel.

Have you measured the tempco-curve of your reference?

But since the REF102 is only available in plastic package the stability will be slightly worse than on the AD587 in CERDIP package.
Attached a picture with ageing drift of a REF102 aginst some AD586LQ. (the small 5V brother of the AD587).
50 deg C constant temperature during measurement.

With best regards

Andreas

[agaelema]

Hi Andreas, thanks for the answer.

Have you measured the tempco-curve of your reference?

- No, how I can do this?

Reading the topics related to precision reference I come to the conclusion that I have much to learn.  Hehe.

Analysing your TC circuit (in the same topic) and doing some simulation I think I understood behaviour.
- the increase in the temperature will decrease the NTC value and this decrease will decrease the voltage applied to the Trim pin, I'm correct?

What is the correct way to calibrate the circuit and select the value of R3 (TC adjust)?

[Andreas]

Hello,

you can either calculate this from datasheet values.
(Trim-range, internal resistors and measured T.C. without adjustment).

But since the values are with large tolerances there is always some trial + error.
Start e.g. with 1 Meg. determine change in T.C.
Double or half the resistor and determine T.C. again.
From this you can calculate the influence more exact and calculate the final R3.

Lars cirquit has the charme that it needs lower power
and you do not have to solder the adjustment resistor.

with best regards

Andreas

[ocw]

I have tested a lot of different voltage references and put together a chart detailing their specifications along with their output voltage as measured on my 34401A.

I tried to list the specification limit, not the "typical" deviation figure.  I didn't want to compare one model's typical as compared to another's maximum.  Occasionally I had to make an educated guess as to its maximum value.  Case-in-point: the beloved LTZ1000.  Linear likes to play up its 0.05ppm/C temperature drift specification without defining it.  It appears to be a typical value.  I guessed that its maximum might be 0.2ppm/C (although it could be 1ppm/C like some other models).  The LTZ1000CH is the only voltage reference detailed on my attachment which I didn't have on hand to measure its actual output voltage.

I colored coded my opinion of the specification.  For example, The LTZ1000 and LM399 have red accuracy specifications, but bright green temperature and long term stability ratings.  I tried to be fair in those ratings and based them on their relative figures compared to the others listed.

The LM4128AMF-3.0 which I tested had a high noise level and poor voltage stability.  It was by far the worst one tested in those regards.

I included a temperature compensated 1N4573A-1 zener in my tests for comparison.  It had good voltage stability and a noise level comparable to the average voltage reference.  The economy BZX79-B6V8,143 zener that I also tested for comparison had both a high noise level and poor voltage stability.

Most of the voltage references tested were purchased either from Mouser, Digi-Key or Arrow.  The two AD584's tested were inside the eBay Chinese boxes which are available.  The AD688BQ was recently obtained from http://www.ebay.com/itm/182537476611 for $18.91 + $4.00 shipping.  It meets its 0.02% voltage accuracy specification for its +/-10V output.  I'll probably add some trimmers to improved that accuracy further.  Its voltage stability has been good in its initial tests.  It's nice not to have to play games to alter the voltage to obtain 10 volts.  Having a similarly accurate 20 volts output can double the precision of tests of some equipment.

Only testing one of most voltage references makes my test of them be not that meaningful.  The LM399AH was the only one where I tested two.  I wish that the tested ISL21009BFB's wouldn't have been discontinued.  The specs of their replacements aren't as good.

Hopefully the attachment is useful for some.  I tried to provide a fair comparison of the different models.  Hopefully I didn't let any typical values slip through and that my approximations of a few maximum specifications aren't too far off the manufacturer's limitations.  Several additional models were just added 6July2017 and 6August2017.  At the bottom of the attached chart I just added the average measured accuracy of all of the voltage references shown which had a specification sheet accuracy of better than 0.10%.  That average accuracy of 0.000486% might be one way of verifying that my Agilent 34401A meter which was used meets its 0.0015% specification sheet accuracy.  35 different voltage references were used in calculating that average.

[ocw]

I originally thought that my measurement of the actual output voltages from the references was important.  Because of that I didn't include the additional voltage references which I had ordered but not yet received or tested.  With the evaluation of generally a single unit not always meaningful, I just added those which I previously deleted.  I just replaced the chart on my prior message with the larger updated one.  Some of the new references added include the AD588BQ, AD587UQ, 1N829A and LT1236ACS8-10.

I also corrected a few errors that I found.  The price color ratings are subjective.  A quality product merits a higher price, although I felt that the noisy LM4128AMF that I tested was over priced at about $2.80.

While I also make semi-regular purchases from Newark, since I'm more likely to make a purchase from the others I didn't include their prices.  The Newark prices aren't generally far off of the others.  I see that there is now a Newark/Arrow connection...

[zhtoor]

I have tested a lot of different voltage references and put together a chart detailing their specifications along with their output voltage as measured on my 34401A.

I tried to list the specification limit, not the "typical" deviation figure.  I didn't want to compare one model's typical as compared to another's maximum.  Occasionally I had to make an educated guess as to its maximum value.  Case-in-point: the beloved LTZ1000.  Linear likes to play up its 0.05ppm/C temperature drift specification without defining it.  It appears to be a typical value.  I guessed that its maximum might be 0.2ppm/C.  The LTZ1000CH is the only voltage reference detailed on my attachment which I didn't have on hand to measure its actual output voltage.

I colored coded my opinion of the specification.  For example, The LTZ1000 and LM399 have red accuracy specifications, but bright green temperature and long term stability ratings.  I tried to be fair in those ratings and based them on their relative figures compared to the others listed.

The LM4128AMF-3.0 which I tested had a high noise level and poor voltage stability.  It was by far the worst one tested in those regards.

I included a temperature compensated 1N4573A-1 zener in my tests for comparison.  It had good voltage stability and a noise level comparable to the average voltage reference.  The economy BZX79-B6V8,143 zener that I also tested for comparison had both a high noise level and poor voltage stability.

Most of the voltage references tested were purchased either from Mouser, Digi-Key or Arrow.  The two AD584's tested were inside the eBay Chinese boxes which are available.  The AD688BQ was recently obtained from http://www.ebay.com/itm/182537476611 for $18.91 + $4.00 shipping.  It meets its 0.02% voltage accuracy specification for its +/-10V output.  I'll probably add some trimmers to improved that accuracy further.  Its voltage stability has been good in its initial tests.  It's nice not to have to play games to alter the voltage to obtain 10 volts.  Having a similarly accurate 20 volts output can double the precision of tests of some equipment.

Only testing one of most voltage references makes my test of them be not that meaningful.  The LM399AH was the only one where I tested two.  I wish that the tested ISL21009BFB's wouldn't have been discontinued.  The specs of their replacements aren't as good.

Hopefully the attachment is useful for some.  I tried to provide a fair comparison of the different models.  Hopefully I didn't let any typical values slip through and that my approximations of a few maximum specifications aren't too far off the manufacturer's limitations.  Several additional models were just added 6July2017.

thanks.

how about LH0070/LT1031B (metal cans)? reportedly pretty good tcr ca. 5ppm and good initial accuracy (+- 3mv for LT1031BMH).

regards.

[Andreas]

I colored coded my opinion of the specification.  For example, The LTZ1000 and LM399 have red accuracy specifications, but bright green temperature and long term stability ratings.

Hello,

be carefully with the long term stability specs:

Some are specified per 1000 hours
others per month. (LT1027)
And some for the 2nd 1000 hours only. (or after pre-conditioning)

Usually they are valid only for the best package of the reference.
(even if the metal can package or the CERDIP package is already obsolete).

with best regards

Andreas

[ocw]

how about LH0070/LT1031B (metal cans)? reportedly pretty good tcr ca. 5ppm and good initial accuracy (+- 3mv for LT1031BMH).

Other than when one is in front of me for testing, I have tried to stay away from listing the obsolete models.  Yes, I know they will probably be available from China as long as there is still demand for them...

Speaking of which, attached are some pictures of my AD688BQ recently received from China.

I have tried to keep all specs to the same standards.  One of my corrections involved changing a uV figure into a PPM number like the others.  Hopefully I have caught all of those.

[GigaJoe]

Need suggestion:

I found nearby AD587LQ -$14 and AD587LN - $2.5

in dilemma: 2-LQ vs 12-LN.
I have a hope , an acrylic conformal coating , a few layers, and metal can fillies with silica where full board will fit in ( thinking of thermos:) ; or sealed metal can ... )  will able to fight with humidity effect for a long term.
adding that with 12 pcs of chip i may have better selective process or do parallel a few

is it a wise, to go with plastic, and adding some humidity countermeasures ?

can someone has opinion to immerse board in some electronic liquid ?

[The Soulman]

If 500ppm (0,05%) of initial accuracy is good enough for you than I'd wouldn't worry about humidity sensitivity to much.
On the other hand if you intend your reference(s) to be measured with lower uncertainty in the future a sealed component would make sense.
 
I have a couple of lt1021DMH10 from Arrow: https://www.arrow.com/en/products/lt1021dmh-10/linear-technology
Poorer initial accuracy but should be pretty stable with time, and not that expensive.

More is always better, but doesn't necessarily help with initial accuracy. 

[Andreas]

is it a wise, to go with plastic, and adding some humidity countermeasures ?

Do you really want to build a humidity sensor with a long (some days) response time?

can someone has opinion to immerse board in some electronic liquid ?

Is that really cheaper (if it works) than using a hermetically package?

And even with hermetically packages you will have to select the best ones for a good reference.

with best regards

Andreas

[GigaJoe]

trying to make something for a long term.
I got LM399 5pcs,   all of them drifting slowly , and 10V amplifier and resistors ...  such a pain .... ( it seems a form of meditation , build something, waiting 5Y, measure , wait another 5  ....)

how big a difference in ppm I may expect from AD587   in cerdip VS plastic if just a humidity factor count, simply count a diff like:   rainy summer (95%) VS sunny winter (30%) ?   


I'm still thinking ... need a case anyway, would be make sense to use 10 in plastic for averaging, and the whole board in a metal container.  like an empty container from the propane can ( or spray) ; filling by silica, the front cover would be PCB with contacts output and power, glued soldered .. inside an inch or 2in of silicone filler. I think it will work ....  I may even consider heater inside,  where ref temp will be LM399.   I'm tend to use a plastic in this construction ...

Thanks for a tip: lt1021DMH10 - interesting option ...

in my understanding a "selection process" from 2 items really sound funny, it seems i ll go to the plastic one; get  it 20-50,  selected items run  in parallel; then all board sealed by some case\process ....

[Andreas]

its just like in the diagram above.

https://www.eevblog.com/forum/metrology/best-out-of-the-box-10v-reference/?action=dlattach;attach=327184;image

The Ref102A is in plastic package : this device has around 5ppm seasonal drift when measured ad 50 deg C.
Rainy summer here is about 60-65% rH
Dry winter about 40% rH.
X-Axis is in day
Y-Axis is in ppm

I have devices up to 0.5ppm / %rH at room temperature in plastic.

with best regards

Andreas

[GigaJoe]

Andreas, thank a lot ...

Seems i toward to the plastic encapsulation , mostly due to quantity i can purchase and selection process,  and trying to mitigate  humidity effect ...

does lt1021 comparable with AD567 for a long term?

Silly question:  wonder, if "soft start" ( V supply rising during seconds may help with accidental Vref shift ? )

[Gyro]

It's probably worth mentioning that $14 is a very good price for the, more or less unobtainable, AD587LQ these days (assuming that they haven't come via China that is).

The TC of the LQ version tends to have a better profile for thermistor compensation around room temperature that the military spec UQ version.

[GigaJoe]

Not sure, if any one here have  interest in AD587LQ version,  I'm not sure a quantity left (it old stock) and seems initial price almost $16.  ( it including sale tax). So PM me if anyone interesting ,  then I will dig further .....

[The Soulman]

does lt1021 comparable with AD567 for a long term?

Silly question:  wonder, if "soft start" ( V supply rising during seconds may help with accidental Vref shift ? )

Both have similar specs.

Soft start only helps if there are capacitors on the output, it will reduce the output current while charging the capacitors.

[eurofox]

My most stable 10V reference at this time is an original Geller SVRT, about 5 years old and was turned ON most of the time.
The picture here shows a recent measurement over night with "cheap normal cables" and around 2 °C change over night.

Actually I am surprised how stable the SVRT really is.
When it is turned off for a few days it needs about 30 h to stabilize again.

Glad that "my" voltage standard got a nice and useful home 

[Insatman]

Greetings,
Attached are graphs of data on a variety of voltage reference ICs I've been testing.  Some have over 1000hrs of data, some less.  Testing is ongoing with a few more types of references to test. 
Note that the VRE305AD was pulled from the test because it clearly was out of spec and replaced by APEX when I sent them the data.  Nice especially since it's a $75 chip. 
One especially nice combination is a AD587UQ with a PTC termistor thermally bonded to it.  The termistor keeps the 587 at about 45C.  The whole mess is mounted in a small ABS box which requires +18VDC at around 30mA.  I plan on building an LTZ1000 down the road but that's a completely new adventure.

[PartialDischarge]

Ok, so a few week ago I finished my heated 10V reference based on the AD588KQ using an enclosure from a broken power supply, this little thing costs 40€ at mouser. It is a handmade prototype with a heated enclosure and I'm still doing modifications but I'm quite happy with it. Here are some results,

-Vertical scale is not the absolute value, I prefer to plot the difference from the mean, in this case in microvolts so really good.
-There is not much difference from the NPLC10 to the NPLC100 and that tells me that noise is not too bad.
-The oscillations are due to the heater turning ON/OFF. I keep it around 40º, but the range is not very tight so still room for improvement here. I'm using a TMP01 so very simple control
-In the NPLC100 measurement the 3458A was still heating so ACAL in the middle clearly did affect the "mean"

Oh, and some details I forgot to mention. The AD588KQ is inside a small hermetic copper can I made for it. On the outside it has a resistive network for adjusting means. This module is contained inside some layers of calcium-magnesium silicate thermal insulation sheet.

[Andreas]

Note that the VRE305AD was pulled from the test because it clearly was out of spec

Hello,

What do you mean with clearly out of spec?
The initial output voltage +1mV against 0.5mV max. (on production, before soldering).
 or the -40 ppm drift over 600 hours against typical 6 ppm/kHr?

Did you also measure 0.1 .. 10 Hz noise?

with best regards

Andreas

[Insatman]

Note that the VRE305AD was pulled from the test because it clearly was out of spec

Hello,

What do you mean with clearly out of spec?
The initial output voltage +1mV against 0.5mV max. (on production, before soldering).
 or the -40 ppm drift over 600 hours against typical 6 ppm/kHr?

Did you also measure 0.1 .. 10 Hz noise?
with best regards

Andreas

It was returned because of initial voltage, but it was also clear the drift was bad as well.  My replacement device was within the initial voltage spec but is drifting way more than specification despite being housed in as ideal environment as I can create for it.  I plan on posting the data in the next month.   I have procured an original Thaler "new old stock" version of the IC recently.  It is currently getting it's initial 200hr burn-in.  I plan on replacing my Apex VRE305 with the Thaler VRE305 in my voltage reference unit. 

A friend who has a lot of experience with these particular references tells me the new Apex devices do not typically meet their drift specifications.  Mine certainly has not.  He says the older Thaler units were quite good, so I'm going to try one I bought from Ebay.  The Apex units short-term tempco appears to be quite low however based on limited data...too bad the long term drift is horrible.  The Apex unit has drifted +150uV since January 3rd of this year.   It's on a very stable clean supply and the trim pot is one of those expensive metal foil type from Vishay.  It is enclosed in an insulated cast aluminum enclosure.   

I am hoping the Thaler unit will provide better performance.  I will know in 6 months or so.   Look for the data on the Apex VRE305 as well as updates on my other references in the next month or so when I get around to updating my Excel speadsheet.

I did not measure the low frequency noise but will do so on my Apex device and Thaler devices for you sometime.  My resolution is limited however as my best meter is an HP34401A. I also have an HP3457A which can average to 7.5digits but I suspect is drifts a bit more than the 34401.   The best standard deviation I can get on the 3457 with any source is around 6.5uV (>1hr measurement window). 

I have recently built a x100 amplifier to measure noise but it has not been well tested as yet.